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Thanks very much, Adam. There were still small spikes visible on the image. It was very unforgiving for any collimation errors as guiding got better. I found one set of screws were a bit tight on the primary mirror cell mount which caused out-focus donuts being half circle on my last imaging session. It used to be with three visible dents before I put the fry-pan ring there. I also tightened secondary mirror spider a bit as I noticed tiny moves of laser beams on centre dot every time which might also have contributed to collimation shifts during imaging sessions, resulting in spiky stars. I saw many great shots with 12 inch Newtonians in this forum, such AG and GSO. I think Skywatcher Newtonians do need much more efforts bringing them to best optical forms. They were just too loosely put together. First of all, centre dots on all my three Skywatcher scopes were off by 2-3 mm. I would recommend anyone owning these scopes to reposition centre dots first. As camera pixels getting smaller and smaller, Newtonians would be good options because of larger F numbers reducing diffraction errors, but all depends on collimation and stiffness of the system holding collimation. John
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